Struct mongodb::Cursor [−][src]
A Cursor
streams the result of a query. When a query is made, a Cursor
will be returned with
the first batch of results from the server; the documents will be returned as the Cursor
is
iterated. When the batch is exhausted and if there are more results, the Cursor
will fetch the
next batch of documents, and so forth until the results are exhausted. Note that because of this
batching, additional network I/O may occur on any given call to Cursor::next
. Because of this,
a Cursor
iterates over Result<Document>
items rather than simply Document
items.
The batch size of the Cursor
can be configured using the options to the method that returns
it. For example, setting the batch_size
field of
FindOptions
will set the batch size of the
Cursor
returned by Collection::find
.
Note that the batch size determines both the number of documents stored in memory by the
Cursor
at a given time as well as the total number of network round-trips needed to fetch all
results from the server; both of these factors should be taken into account when choosing the
optimal batch size.
A cursor can be used like any other Stream
. The simplest way is just to iterate over the
documents it yields:
while let Some(doc) = cursor.next().await { println!("{}", doc?) }
Additionally, all the other methods that an Stream
has are available on Cursor
as well.
This includes all of the functionality provided by StreamExt
, which provides similar functionality to the standard library Iterator
trait.
For instance, if the number of results from a query is known to be small, it might make sense
to collect them into a vector:
let results: Vec<Result<Document>> = cursor.collect().await;
Trait Implementations
impl<T: Debug> Debug for Cursor<T> where
T: DeserializeOwned + Unpin,
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T: DeserializeOwned + Unpin,
impl<T> Drop for Cursor<T> where
T: DeserializeOwned + Unpin,
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T: DeserializeOwned + Unpin,
impl<T> Stream for Cursor<T> where
T: DeserializeOwned + Unpin,
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T: DeserializeOwned + Unpin,
Auto Trait Implementations
impl<T = Document> !RefUnwindSafe for Cursor<T>
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impl<T> Send for Cursor<T> where
T: Send,
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T: Send,
impl<T = Document> !Sync for Cursor<T>
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impl<T> Unpin for Cursor<T>
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impl<T = Document> !UnwindSafe for Cursor<T>
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Blanket Implementations
impl<T> Any for T where
T: 'static + ?Sized,
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T: 'static + ?Sized,
impl<T> Borrow<T> for T where
T: ?Sized,
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T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
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T: ?Sized,
pub fn borrow_mut(&mut self) -> &mut T
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impl<T> From<T> for T
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impl<T> Instrument for T
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pub fn instrument(self, span: Span) -> Instrumented<Self>
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pub fn in_current_span(self) -> Instrumented<Self>
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impl<T> Instrument for T
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pub fn instrument(self, span: Span) -> Instrumented<Self>
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pub fn in_current_span(self) -> Instrumented<Self>
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impl<T, U> Into<U> for T where
U: From<T>,
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U: From<T>,
impl<T> Same<T> for T
type Output = T
Should always be Self
impl<St> StreamExt for St where
St: Stream + ?Sized,
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St: Stream + ?Sized,
pub fn next(&mut self) -> Next<'_, Self> where
Self: Unpin,
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Self: Unpin,
pub fn try_next<T, E>(&mut self) -> TryNext<'_, Self> where
Self: Stream<Item = Result<T, E>> + Unpin,
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Self: Stream<Item = Result<T, E>> + Unpin,
pub fn map<T, F>(self, f: F) -> Map<Self, F> where
F: FnMut(Self::Item) -> T,
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F: FnMut(Self::Item) -> T,
pub fn merge<U>(self, other: U) -> Merge<Self, U> where
U: Stream<Item = Self::Item>,
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U: Stream<Item = Self::Item>,
pub fn filter<F>(self, f: F) -> Filter<Self, F> where
F: FnMut(&Self::Item) -> bool,
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F: FnMut(&Self::Item) -> bool,
pub fn filter_map<T, F>(self, f: F) -> FilterMap<Self, F> where
F: FnMut(Self::Item) -> Option<T>,
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F: FnMut(Self::Item) -> Option<T>,
pub fn fuse(self) -> Fuse<Self>
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pub fn take(self, n: usize) -> Take<Self>
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pub fn take_while<F>(self, f: F) -> TakeWhile<Self, F> where
F: FnMut(&Self::Item) -> bool,
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F: FnMut(&Self::Item) -> bool,
pub fn skip(self, n: usize) -> Skip<Self>
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pub fn skip_while<F>(self, f: F) -> SkipWhile<Self, F> where
F: FnMut(&Self::Item) -> bool,
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F: FnMut(&Self::Item) -> bool,
pub fn all<F>(&mut self, f: F) -> AllFuture<'_, Self, F> where
Self: Unpin,
F: FnMut(Self::Item) -> bool,
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Self: Unpin,
F: FnMut(Self::Item) -> bool,
pub fn any<F>(&mut self, f: F) -> AnyFuture<'_, Self, F> where
Self: Unpin,
F: FnMut(Self::Item) -> bool,
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Self: Unpin,
F: FnMut(Self::Item) -> bool,
pub fn chain<U>(self, other: U) -> Chain<Self, U> where
U: Stream<Item = Self::Item>,
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U: Stream<Item = Self::Item>,
pub fn fold<B, F>(self, init: B, f: F) -> FoldFuture<Self, B, F> where
F: FnMut(B, Self::Item) -> B,
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F: FnMut(B, Self::Item) -> B,
pub fn collect<T>(self) -> Collect<Self, T> where
T: FromStream<Self::Item>,
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T: FromStream<Self::Item>,
pub fn timeout(self, duration: Duration) -> Timeout<Self>
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impl<T> StreamExt for T where
T: Stream + ?Sized,
T: Stream + ?Sized,
pub fn next(&mut self) -> Next<'_, Self> where
Self: Unpin,
Self: Unpin,
pub fn into_future(self) -> StreamFuture<Self> where
Self: Unpin,
Self: Unpin,
pub fn map<T, F>(self, f: F) -> Map<Self, F> where
F: FnMut(Self::Item) -> T,
F: FnMut(Self::Item) -> T,
pub fn enumerate(self) -> Enumerate<Self>
pub fn filter<Fut, F>(self, f: F) -> Filter<Self, Fut, F> where
F: FnMut(&Self::Item) -> Fut,
Fut: Future<Output = bool>,
F: FnMut(&Self::Item) -> Fut,
Fut: Future<Output = bool>,
pub fn filter_map<Fut, T, F>(self, f: F) -> FilterMap<Self, Fut, F> where
F: FnMut(Self::Item) -> Fut,
Fut: Future<Output = Option<T>>,
F: FnMut(Self::Item) -> Fut,
Fut: Future<Output = Option<T>>,
pub fn then<Fut, F>(self, f: F) -> Then<Self, Fut, F> where
F: FnMut(Self::Item) -> Fut,
Fut: Future,
F: FnMut(Self::Item) -> Fut,
Fut: Future,
pub fn collect<C>(self) -> Collect<Self, C> where
C: Default + Extend<Self::Item>,
C: Default + Extend<Self::Item>,
pub fn unzip<A, B, FromA, FromB>(self) -> Unzip<Self, FromA, FromB> where
Self: Stream<Item = (A, B)>,
FromA: Default + Extend<A>,
FromB: Default + Extend<B>,
Self: Stream<Item = (A, B)>,
FromA: Default + Extend<A>,
FromB: Default + Extend<B>,
pub fn concat(self) -> Concat<Self> where
Self::Item: Extend<<Self::Item as IntoIterator>::Item>,
Self::Item: IntoIterator,
Self::Item: Default,
Self::Item: Extend<<Self::Item as IntoIterator>::Item>,
Self::Item: IntoIterator,
Self::Item: Default,
pub fn cycle(self) -> Cycle<Self> where
Self: Clone,
Self: Clone,
pub fn fold<T, Fut, F>(self, init: T, f: F) -> Fold<Self, Fut, T, F> where
F: FnMut(T, Self::Item) -> Fut,
Fut: Future<Output = T>,
F: FnMut(T, Self::Item) -> Fut,
Fut: Future<Output = T>,
pub fn flatten(self) -> Flatten<Self> where
Self::Item: Stream,
Self::Item: Stream,
pub fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> where
F: FnMut(Self::Item) -> U,
U: Stream,
F: FnMut(Self::Item) -> U,
U: Stream,
pub fn scan<S, B, Fut, F>(self, initial_state: S, f: F) -> Scan<Self, S, Fut, F> where
F: FnMut(&mut S, Self::Item) -> Fut,
Fut: Future<Output = Option<B>>,
F: FnMut(&mut S, Self::Item) -> Fut,
Fut: Future<Output = Option<B>>,
pub fn skip_while<Fut, F>(self, f: F) -> SkipWhile<Self, Fut, F> where
F: FnMut(&Self::Item) -> Fut,
Fut: Future<Output = bool>,
F: FnMut(&Self::Item) -> Fut,
Fut: Future<Output = bool>,
pub fn take_while<Fut, F>(self, f: F) -> TakeWhile<Self, Fut, F> where
F: FnMut(&Self::Item) -> Fut,
Fut: Future<Output = bool>,
F: FnMut(&Self::Item) -> Fut,
Fut: Future<Output = bool>,
pub fn take_until<Fut>(self, fut: Fut) -> TakeUntil<Self, Fut> where
Fut: Future,
Fut: Future,
pub fn for_each<Fut, F>(self, f: F) -> ForEach<Self, Fut, F> where
F: FnMut(Self::Item) -> Fut,
Fut: Future<Output = ()>,
F: FnMut(Self::Item) -> Fut,
Fut: Future<Output = ()>,
pub fn for_each_concurrent<Fut, F>(
self,
limit: impl Into<Option<usize>>,
f: F
) -> ForEachConcurrent<Self, Fut, F> where
F: FnMut(Self::Item) -> Fut,
Fut: Future<Output = ()>,
self,
limit: impl Into<Option<usize>>,
f: F
) -> ForEachConcurrent<Self, Fut, F> where
F: FnMut(Self::Item) -> Fut,
Fut: Future<Output = ()>,
pub fn take(self, n: usize) -> Take<Self>
pub fn skip(self, n: usize) -> Skip<Self>
pub fn fuse(self) -> Fuse<Self>
pub fn by_ref(&mut self) -> &mut Self
pub fn catch_unwind(self) -> CatchUnwind<Self> where
Self: UnwindSafe,
Self: UnwindSafe,
pub fn boxed<'a>(
self
) -> Pin<Box<dyn Stream<Item = Self::Item> + 'a + Send, Global>> where
Self: Send + 'a,
self
) -> Pin<Box<dyn Stream<Item = Self::Item> + 'a + Send, Global>> where
Self: Send + 'a,
pub fn boxed_local<'a>(
self
) -> Pin<Box<dyn Stream<Item = Self::Item> + 'a, Global>> where
Self: 'a,
self
) -> Pin<Box<dyn Stream<Item = Self::Item> + 'a, Global>> where
Self: 'a,
pub fn buffered(self, n: usize) -> Buffered<Self> where
Self::Item: Future,
Self::Item: Future,
pub fn buffer_unordered(self, n: usize) -> BufferUnordered<Self> where
Self::Item: Future,
Self::Item: Future,
pub fn zip<St>(self, other: St) -> Zip<Self, St> where
St: Stream,
St: Stream,
pub fn chain<St>(self, other: St) -> Chain<Self, St> where
St: Stream<Item = Self::Item>,
St: Stream<Item = Self::Item>,
pub fn peekable(self) -> Peekable<Self>
pub fn chunks(self, capacity: usize) -> Chunks<Self>
pub fn ready_chunks(self, capacity: usize) -> ReadyChunks<Self>
pub fn forward<S>(self, sink: S) -> Forward<Self, S> where
Self: TryStream,
S: Sink<Self::Ok, Error = Self::Error>,
Self: TryStream,
S: Sink<Self::Ok, Error = Self::Error>,
pub fn split<Item>(self) -> (SplitSink<Self, Item>, SplitStream<Self>) where
Self: Sink<Item>,
Self: Sink<Item>,
pub fn inspect<F>(self, f: F) -> Inspect<Self, F> where
F: FnMut(&Self::Item),
F: FnMut(&Self::Item),
pub fn left_stream<B>(self) -> Either<Self, B> where
B: Stream<Item = Self::Item>,
B: Stream<Item = Self::Item>,
pub fn right_stream<B>(self) -> Either<B, Self> where
B: Stream<Item = Self::Item>,
B: Stream<Item = Self::Item>,
pub fn poll_next_unpin(
&mut self,
cx: &mut Context<'_>
) -> Poll<Option<Self::Item>> where
Self: Unpin,
&mut self,
cx: &mut Context<'_>
) -> Poll<Option<Self::Item>> where
Self: Unpin,
pub fn select_next_some(&mut self) -> SelectNextSome<'_, Self> where
Self: Unpin + FusedStream,
Self: Unpin + FusedStream,
impl<T, U> TryFrom<U> for T where
U: Into<T>,
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U: Into<T>,
type Error = Infallible
The type returned in the event of a conversion error.
pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
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impl<T, U> TryInto<U> for T where
U: TryFrom<T>,
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U: TryFrom<T>,
type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
pub fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
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impl<S, T, E> TryStream for S where
S: Stream<Item = Result<T, E>> + ?Sized,
S: Stream<Item = Result<T, E>> + ?Sized,
type Ok = T
The type of successful values yielded by this future
type Error = E
The type of failures yielded by this future
pub fn try_poll_next(
self: Pin<&mut S>,
cx: &mut Context<'_>
) -> Poll<Option<Result<<S as TryStream>::Ok, <S as TryStream>::Error>>>
self: Pin<&mut S>,
cx: &mut Context<'_>
) -> Poll<Option<Result<<S as TryStream>::Ok, <S as TryStream>::Error>>>
impl<S> TryStreamExt for S where
S: TryStream + ?Sized,
S: TryStream + ?Sized,
pub fn err_into<E>(self) -> ErrInto<Self, E> where
Self::Error: Into<E>,
Self::Error: Into<E>,
pub fn map_ok<T, F>(self, f: F) -> MapOk<Self, F> where
F: FnMut(Self::Ok) -> T,
F: FnMut(Self::Ok) -> T,
pub fn map_err<E, F>(self, f: F) -> MapErr<Self, F> where
F: FnMut(Self::Error) -> E,
F: FnMut(Self::Error) -> E,
pub fn and_then<Fut, F>(self, f: F) -> AndThen<Self, Fut, F> where
F: FnMut(Self::Ok) -> Fut,
Fut: TryFuture<Error = Self::Error>,
F: FnMut(Self::Ok) -> Fut,
Fut: TryFuture<Error = Self::Error>,
pub fn or_else<Fut, F>(self, f: F) -> OrElse<Self, Fut, F> where
F: FnMut(Self::Error) -> Fut,
Fut: TryFuture<Ok = Self::Ok>,
F: FnMut(Self::Error) -> Fut,
Fut: TryFuture<Ok = Self::Ok>,
pub fn inspect_ok<F>(self, f: F) -> InspectOk<Self, F> where
F: FnMut(&Self::Ok),
F: FnMut(&Self::Ok),
pub fn inspect_err<F>(self, f: F) -> InspectErr<Self, F> where
F: FnMut(&Self::Error),
F: FnMut(&Self::Error),
pub fn into_stream(self) -> IntoStream<Self>
pub fn try_next(&mut self) -> TryNext<'_, Self> where
Self: Unpin,
Self: Unpin,
pub fn try_for_each<Fut, F>(self, f: F) -> TryForEach<Self, Fut, F> where
F: FnMut(Self::Ok) -> Fut,
Fut: TryFuture<Ok = (), Error = Self::Error>,
F: FnMut(Self::Ok) -> Fut,
Fut: TryFuture<Ok = (), Error = Self::Error>,
pub fn try_skip_while<Fut, F>(self, f: F) -> TrySkipWhile<Self, Fut, F> where
F: FnMut(&Self::Ok) -> Fut,
Fut: TryFuture<Ok = bool, Error = Self::Error>,
F: FnMut(&Self::Ok) -> Fut,
Fut: TryFuture<Ok = bool, Error = Self::Error>,
pub fn try_take_while<Fut, F>(self, f: F) -> TryTakeWhile<Self, Fut, F> where
F: FnMut(&Self::Ok) -> Fut,
Fut: TryFuture<Ok = bool, Error = Self::Error>,
F: FnMut(&Self::Ok) -> Fut,
Fut: TryFuture<Ok = bool, Error = Self::Error>,
pub fn try_for_each_concurrent<Fut, F>(
self,
limit: impl Into<Option<usize>>,
f: F
) -> TryForEachConcurrent<Self, Fut, F> where
F: FnMut(Self::Ok) -> Fut,
Fut: Future<Output = Result<(), Self::Error>>,
self,
limit: impl Into<Option<usize>>,
f: F
) -> TryForEachConcurrent<Self, Fut, F> where
F: FnMut(Self::Ok) -> Fut,
Fut: Future<Output = Result<(), Self::Error>>,
pub fn try_collect<C>(self) -> TryCollect<Self, C> where
C: Default + Extend<Self::Ok>,
C: Default + Extend<Self::Ok>,
pub fn try_filter<Fut, F>(self, f: F) -> TryFilter<Self, Fut, F> where
F: FnMut(&Self::Ok) -> Fut,
Fut: Future<Output = bool>,
F: FnMut(&Self::Ok) -> Fut,
Fut: Future<Output = bool>,
pub fn try_filter_map<Fut, F, T>(self, f: F) -> TryFilterMap<Self, Fut, F> where
F: FnMut(Self::Ok) -> Fut,
Fut: TryFuture<Ok = Option<T>, Error = Self::Error>,
F: FnMut(Self::Ok) -> Fut,
Fut: TryFuture<Ok = Option<T>, Error = Self::Error>,
pub fn try_flatten(self) -> TryFlatten<Self> where
Self::Ok: TryStream,
<Self::Ok as TryStream>::Error: From<Self::Error>,
Self::Ok: TryStream,
<Self::Ok as TryStream>::Error: From<Self::Error>,
pub fn try_fold<T, Fut, F>(self, init: T, f: F) -> TryFold<Self, Fut, T, F> where
F: FnMut(T, Self::Ok) -> Fut,
Fut: TryFuture<Ok = T, Error = Self::Error>,
F: FnMut(T, Self::Ok) -> Fut,
Fut: TryFuture<Ok = T, Error = Self::Error>,
pub fn try_concat(self) -> TryConcat<Self> where
Self::Ok: Extend<<Self::Ok as IntoIterator>::Item>,
Self::Ok: IntoIterator,
Self::Ok: Default,
Self::Ok: Extend<<Self::Ok as IntoIterator>::Item>,
Self::Ok: IntoIterator,
Self::Ok: Default,
pub fn try_buffer_unordered(self, n: usize) -> TryBufferUnordered<Self> where
Self::Ok: TryFuture,
<Self::Ok as TryFuture>::Error == Self::Error,
Self::Ok: TryFuture,
<Self::Ok as TryFuture>::Error == Self::Error,
pub fn try_buffered(self, n: usize) -> TryBuffered<Self> where
Self::Ok: TryFuture,
<Self::Ok as TryFuture>::Error == Self::Error,
Self::Ok: TryFuture,
<Self::Ok as TryFuture>::Error == Self::Error,
pub fn try_poll_next_unpin(
&mut self,
cx: &mut Context<'_>
) -> Poll<Option<Result<Self::Ok, Self::Error>>> where
Self: Unpin,
&mut self,
cx: &mut Context<'_>
) -> Poll<Option<Result<Self::Ok, Self::Error>>> where
Self: Unpin,
pub fn into_async_read(self) -> IntoAsyncRead<Self> where
Self: TryStreamExt<Error = Error> + Unpin,
Self::Ok: AsRef<[u8]>,
Self: TryStreamExt<Error = Error> + Unpin,
Self::Ok: AsRef<[u8]>,
impl<V, T> VZip<V> for T where
V: MultiLane<T>,
V: MultiLane<T>,